The present invention relates to a thermal transfer recording medium for use in thermal transfer recording devices such as thermal printers and facsimile terminal equipment. More particularly, the present invention relates to a thermal transfer recording medium for use in formation of a multi-color or full-color image by superimposing-transfer of plural different color inks.
Hitherto there has been performed the formation of a multi-color or full-color image involving a region developing a color by virtue of subtractive color mixture wherein plural different color inks are superimposingly transferred one on another on a receptor by means of a thermal transfer printer or the like. As the thermal transfer recording medium for such a method there has been widely used one having the structure wherein a release layer comprising a wax as a main ingredient is interposed between a foundation and a color ink layer to improve the transferability.
When plural different color inks are superimposingly transferred to form a multi-color or full-color image on a receptor by use of the above-mentioned thermal transfer recording medium, the release layer comprising a wax as a main ingredient would exist on the top of first color ink dots formed on the receptor, causing the problem wherein second color ink dots are not satisfactorily superimposed onto the first color ink dots due to the presence of the release layer on the first color ink dots.
In view of the aforesaid problem of the prior art, it is an object of the present invention to provide a novel technique wherein, in forming a color image by use of a thermal transfer recording medium having the structure wherein a release layer comprising a wax as a main ingredient is interposed between a foundation and a color ink layer, second color ink dots can be satisfactorily transferred onto first color ink dots.
This and other objects of the present invention will become apparent from the description hereinafter.
The present invention provides a thermal transfer recording medium for forming a color image by superimposingly transferring plural different color inks, comprising a foundation and a first and second color ink layer provided on the foundation, and a first and second release layer comprising a wax interposed between the foundation and the respective color ink layers,
wherein the heat of fusion C1 of the release layer for a first color and the heat of fusion C2 of the release layer for a second color satisfy the relationship represented by formula (I):
C1 less than C2xe2x80x83xe2x80x83(I). 
According to an embodiment of the present invention, the heat of fusion C1 of the release layer for a first color preferably satisfies the relationship represented by formula (II):
160 mJ/mgxe2x89xa7C1xe2x80x83xe2x80x83(II). 
According to another embodiment of the present invention, the heat of fusion C1 of the release layer for a first color and the heat of fusion C2 of the release layer for a second color preferably satisfy the relationship represented by formula (III):
30 mJ/mgxe2x89xa6C2xe2x88x92C1xe2x80x83xe2x80x83(III). 
According to a further embodiment of the present invention, plural different color ink layers are disposed in a side-by-side relation on single foundation with respective release layers intervening therebetween.
According to still further embodiment of the present invention, plural different color ink layers are disposed on separate foundations with respective release layers intervening therebetween.